In the Midwest U.S. state of Illinois, state and federal wildlife officials are pinning their hopes on an experimental barrier in their effort to keep a potentially damaging fish out of Lake Michigan. The barrier is designed to repel fish using small amounts of electricity. Officials have just a few months to make last-minute adjustments to the structure.
The barrier is located in a shipping canal, about 50-kilometers southwest of Chicago and Lake Michigan. A series of cables strung across the bottom of the canal send out steady pulses of electricity, strong enough to repel a fish without hurting it, but strong enough to interfere with my tape recorder if I stand too close.
The barrier was turned on about six-months ago, to see whether such a device could keep fish from crossing between the Great Lakes and the Mississippi River. Jerry Rasmussen, a coordinator for the Mississippi Interstate Conservation Resource Association, says "this is the main line of defense. If the barrier has a use, its use is to keep these Asian carp out."
The Asian carp is actually four species of carp, all introduced to the United States from China or Eastern Siberia about 30 years ago to help control plant growth in commercial fish ponds in the Southern United States. They have escaped those fish farms due to floods and intentional release, and have proliferated along the Mississippi River and its tributaries. John Rogner with the U.S. Fish and Wildlife Service says it has been devastating to native fish populations. "It has displaced our native fish, especially in the Mississippi [River] and the backwaters," he says. "In some places, almost 100-percent displacement of native fish by these Asian carp."
The carp does this by eating lots of the food native fish eat when they are young - plankton, algae and insect larvae. Mr. Rasmussen says Asian carp species reproduce rapidly and in large numbers, and grow to weigh as much as 65 kilograms. Adults eat almost half their body weight in food every day, threatening other species. "Every larval fish has to start out eating plankton before they get up to eating bigger things," he says. "These things [Asian Carp] consume all of that. They will impact every native game fish, sport fish of any kind."
Until about 100 years ago, the Mississippi River and the Great Lakes were not connected. But in the early 20th century, Chicago built a shipping canal to connect the two. It allowed freight to float from Chicago to the Gulf of Mexico, but also allows aquatic life to pass between the two water systems.
Beldon McPheron, with the U.S. Army Corps of Engineers, which operates the fish barrier, says "this waterway serves as the sole link, the sole waterway link, between the Great Lakes basin and the Mississippi River basin. This is an ideal place to put it."
Conservation experts hope the barrier would also keep the round goby, a much smaller nuisance fish, from leaving the Great Lakes for the Mississippi River. But, goby had already passed the electric barrier by the time it was activated.
Officials say they still have time to stop the Asian carp. The closest ones to Chicago are in the Illinois River, about 30-kilometers downstream from the barrier. They should reach it by next June.
John Dettmers with the Illinois Natural History Survey says officials are testing the barrier using a common, non-threatening species of carp. "Essentially what we are doing is putting transmitters in the fish and releasing them either upstream or downstream of the barrier, and then trying to track them to see if they cross the barrier or not," he says.
So far, none of the "test carp" has crossed the barrier. Officials are installing a backup generator that will keep the barrier functioning if the power goes out locally. They also want to build a second electric barrier nearby for times when the first one has to be shut down for maintenance.